By that time, Bass had already abandoned his legal career to write two screenplays for Fox at $125,000 each. Though neither would make it to the screen, his scripts for Arthur Penn's "Target" (1985), Bob Rafelson's "Black Widow" and Francis Ford Coppola's "Gardens of Stone" (both 1987) did. In collaboration with Barry Morrow, Bass enjoyed a career breakthrough as well as blockbuster success with Barry Levinson's "Rain Man" (1988), for which he shared the Oscar for Best Original Screenplay. He enjoyed another hit with the Julia Roberts thriller "Sleeping With the Enemy" (1991) and surprising success with his adaptation with Amy Tan of her novel "The Joy Luck Club" (1993), which gave Bass his first producing credit. His commercial streak faltered with the comedy-drama "When a Man Loves a Woman" (1994), starring Meg Ryan as an alcoholic mother, but resumed with the Michelle Pfeiffer social problem picture "Dangerous Minds" (1995). Bass finished out that year executive producing the eagerly awaited "Waiting to Exhale", which he adapted with novelist and fellow executive producer Terry McMillan. Like "The Joy Luck Club", the film told a culturally specific story of women and their problems with their men. In fact, many in Hollywood credit him with single-handedly inventing the "woman's picture" of the 90s.
After a sojourn in television, where he served as co-executive producer and creator of both the ABC series version of "Dangerous Minds" (1996-1997, based on the feature) and the CBS drama "Moloney" (1996-97), Bass returned to features with the comedy "My Best Friend's Wedding" (1997), a brittle and witty story about a restaurant critic (Julia Roberts) who schemes to break up the impending nuptials of her college beau. Preview audiences persuaded Bass to make two important changes. Roberts had to properly atone for trying to steal Cameron Diaz's fiance, and her gay friend George (Rupert Everett) had to return at movie's end because the surveys had indicated it was their relationship that mattered. The film was a box-office hit, restoring luster to Roberts' star and earning critical raves for its somewhat subversive take on screwball comedies. He reteamed with McMillan for "How Stella Got Her Groove Back" (1998), though its box office success fell far short of "Waiting to Exhale". He demonstrated how comfortably he could excel in almost any genre by ably tackling Jon Amiel's caper comedy "Entrapment" (1999) and kept his hand in television as co-writer of three TV-movies airing in 1999: "Swing Vote" (ABC), "Border Line" (NBC) and "Invisible Child" (Lifetime).
After five other writers had tackled the story, it was Bass' draft of "Stepmom" (1998) that introduced the all-important third-act conflict between the cancer-ridden mother and the father's fiance, persuading Roberts and Susan Sarandon to commit to the film. The film's box office gross of well in excess of $100 million meant that three of Bass' most profitable pictures had starred Roberts. Though he has it in his contract that his words (in an original screenplay) cannot be altered without his permission, his work often changes in the hands of the director. "Snow Falling on Cedars" (1999) was a perfect example as helmer Scott Hicks (in collaboration with original author David Guterson) removed the voice-overs and focused more on the novel's love story, resulting in what Bass called "more poetic and impressionistic, less literal and direct." (Los Angeles Times, December 12, 1999). His exclusive deal with Sony means he often troubleshoots on movies for which he will never receive credit, thus continuing a tradition that by the spring of 1999 had seen him contribute, in one form or another, to more than 100 film and TV projects.